This invention relates to the manufacture of cellular rubber products, with either open or closed pores, but preferably products made from open pore sponge rubber or foam rubber.
More particularly the invention relates to manufacture of spherical sponges, which are circulated through the tubes of heat exchangers to clean the inner surfaces of the tubes, as described in Taprogge U.S. Pat. No. 2,801,824, particularly Column 4, lines 7 to 27.
Cellular rubber such as ordinary rubber sponge tends to have a skin, and when the sponges are to be used for cleaning, they must be trimmed to remove the skin and expose the cut edges of the rubber partitions which enclose the pores, since it is the edges which are effective in scrubbing fouled surfaces. Consequently, sponges are ordinarily made oversize and trimmed to the desired size and shape.
Trimming of rubber sponges having a doubly curved surface has been a slow and expensive procedure, since the rubber sponge is flimsy and difficult to support adequately while it is being trimmed to the desired size and shape, particularly if the sponge product is about an inch (25 mm) or less in over-all size.